L6-8: DNA Structure, Replication and Mutation Flashcards Preview

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Flashcards in L6-8: DNA Structure, Replication and Mutation Deck (27)
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1

Four hypotheses of origin of life on earth

1. synthesis in reducing atmosphere
2. meteorites (panspermia)
3. synthesis in deep ocean vents
4. RNA

2

what are control regions on DNA

specific sequences not in triplets

3

diff. in the ribose b/w DNA and RNA

dna= h
rna= oh

4

how are polymers of nucleic acids linked

5' phosphate + 3' OH
Phosphodiester bond

5

what is Z dna

left handed

6

two strands in replication

leading and lagging

7

what is the short segments in lagging strand called

okazaki fragments

8

what is the first step of DNA repliction

helicase unwinds at origin

9

explain step 2: dna primase and rna primer

dna primase synthesises short short of RNA primer= adds several nucleotides to ss to kick off rpelication

10

explain step 3: dna polymerase

DNA polymerase adds nucleotide to 3' hydroxyl end of RNA primer

11

explain step 4 b: lagging strand

okazaki fragments primed in several spots using RNA primer + dna polymerase adds nucleotides
dna ligase joined fragments by sugar phosphate backbone

12

explain 4 proteins in replication machine

SS DNA binding proteins= stabalise ss
helicase= unwinds = ss
sliding clamp= holds dna polymerase on dna
clamp loader= assembles clamp using atp

13

2 ways changes in DNA sequence occur

1. DNA replication errors
2. environmental factors

14

what is DNAs high fidelity caused by

1. base pair structures
2. primer requirements of dna polymerase
3. dna polymerase proof reads

15

3 types of environmental factors effecting dna sequences changing

chemical
radiation
mobile dna

16

two forms of nucleotide instability

1. depurination: loss of G or A= gap
2. deamination= loss of amino group = C > U

17

Two mutagenic chemical mutations

alkylation: electrophiles add alkyl groups to nitro bases
intercalation: compound inserts into double stranded helix

18

wat does uv light do to dna

attach two adjacent thymine= thymine dimer

19

two ways gamma and x rays attack dna bonds

directly
indirectly
= results in single and double strand breaking

20

when do mobile genetic elements insert into dna

recombination
- breaking and rejoining of DNA during = nonhomogous recom + homo recom

21

what are transposons (tn)

linear dna that insert into dna sequences

22

two types of transposition mechanisms

1. cut and past
2. replicative transposition

23

2 dna repair mechanisms

mismatch pair (correct dna polymerase mistakes)
homologous recombination = repairs double stranded brakes

24

how does mismatch repair

'mis paired nucleotides'
four steps
1. Excision by nucleases
2, Re-synthesis by repair DNA polymerase
3. Ligation of the DNA backbone by DNA ligase

25

how does homologous recombination repair

exonuclease removes nucleotides
ss 3' overhang and migrate into recipient
rna polymerase = new strand
rotation of crossed strands

26

what is holliday junction

crossed strands during homo recom

27

enzymes in hr

exonuclease + dna polymerase